Moveable barriers such as sectional doors have been used for years in association with utility buildings and residential garages. For convenience purposes, it is well known to provide such sectional doors with operator mechanisms including motors to facilitate opening and closing of the door. Moreover, a controller is provided to control operation of the operator mechanisms.
Normally, a controller is equipped with a safety subroutine used during the closing cycle of the sectional door. The safety subroutine responds when an obstruction is sensed in the path of the sectional door. For example, a force sensor is provided to sense forces resisting the movement of the sectional door. The force sensor provides sensor readings to the controller, and the sensor readings are compared to a response threshold.
The response threshold is set slightly above the force normally used by the operator mechanism to close the sectional door. If the sensor readings have values below the response threshold, then the controller instructs the operator mechanism to continue operation. However, if the sensor readings have values above the response threshold, then the controller deactivates operation of the operator mechanism.
Because there can be significant differences between normal resistance forces along the length of the sectional door's travel from the opened position to the closed position, and the response threshold of the safety subroutine, the sensitivity of the safety subroutine varies.
For example, when the normal resistance to movement of the sectional door is high, the difference between the readings of the force sensor and the response threshold is small. Therefore, when the normal resistance to movement of the sectional door is high, the safety subroutine is very sensitive because only a small force due to an obstruction is required to push the sensor readings past the response threshold. However, when the normal resistance to movement of the sectional door is low, the difference between the readings of the force sensor and the response threshold is large. Therefore, when the normal resistance to movement of the sectional door is low, the safety subroutine is not very sensitive because a large obstruction force is required to push the sensor reading past the response threshold.
During most of the length of travel of the sectional door from the opened position to the closed position, the sensitivity of the safety subroutine is immaterial because movement of the sectional door will push an obstruction out of its path. However, during the final portion of travel (from approximately twelve (12) inches above the ground to the ground), which is appropriately named the “danger zone,” it is possible for children and small animals to be trapped underneath the sectional door. However, because the normal resistance to movement of the sectional door during travel through the danger zone is low, the sensitivity of the safety subroutine during such travel is also low. Therefore, a large obstruction force would be necessary to push the sensor reading past the response threshold during travel of the sectional door through the danger zone.
The large obstruction force necessary to “trip” the safety routine translates into a longer period of time children or small animals may be trapped beneath the sectional door before the safety routine is actuated. As such, the lack of sensitivity of the safety routine during the travel of the sectional door through the danger zone is potentially dangerous.
Therefore, there is a need for a controller capable of varying the operator force, and hence, varying the response threshold of the safety subroutine, during the final portion of travel of the sectional door.